This invention relates to heaters, in particular to heaters for heating the coolant of vehicles and to controls therefor.
Fuel-powered vehicle heaters are used for two main purposes. The first purpose is to heat the coolant of the vehicle so the vehicle is easier to start in cold climates. This is particularly important for diesel-powered vehicles which are often difficult to start due to low volatility of the fuel. However these heaters have a second important function, particularly for transit vehicles such as buses. Heaters relying solely on the engine coolant as heated by the engine may be insufficient to provide a comfortable interior temperature. Accordingly, fuel-powered heaters may be used to supplement the heat by providing additional heat to the coolant.
Fuel-powered vehicle heaters conventionally include a combustion chamber surrounded by a coolant jacket where the coolant is heated by combustion of fuel in the combustion chamber. There is a burner head assembly connected to the combustion chamber which includes such components as a combustion fan, an electric motor for the fan, a burner, a compressor for supplying compressed air to the burner, a fuel pump and a control module. The compressor and the fuel pump are typically operated by the motor. In some prior art heaters the control module is mounted as an exterior unit on the burner head assembly.
Typical prior art vehicle heaters employ fans with motors which lack speed control. Accordingly the output of the fan, the compressor, the fuel pump and accordingly of the heater, is dictated to some extent by the voltage supplied to the heater, which can vary as much as 50 percent. Thus a steady output from the heater is not assured.
Also, prior art motors have conventionally been customized for the voltage available from the vehicle, typically 12 volts or 24 volts. This means that different motors have been required for these different voltage applications.
Different heat outputs may be required for different vehicles. For example, larger buses require heaters with higher BTU outputs than smaller buses. Manufacturers have had to supply completely different heaters for these different heating requirements and this increases the cost of manufacture as well as the complexity and cost of warehousing and handling different models of heaters.
Another problem associated with prior art vehicle heaters is troubleshooting techniques. Some prior art vehicle heaters require special diagnostic tools. These heaters do not allow for easily testing and diagnosing of problems arising with various components of the heater.
One problem encountered with prior art heaters is ascertaining whether or not proper combustion is occurring. Typically a sight glass is provided which allows an operator or technician to view the combustion area and therefore check for the presence or absence of a flame. The operator/technician can effectively troubleshoot the flame sensor assembly and heater control and replace either if required. It is desirable to remove the sight glass in order to simplify the construction of the heater, but this leaves a problem of how to properly check the flame.
Coolant pumps for vehicle heaters sometimes have a maximum current limit which may be exceeded when the motor starts. It is feasible to use a “soft start” which starts and stops the current very quickly, somewhat analogous to pulse width modulation, when an overcurrent is sensed. However such a soft start may cause chattering of the relay associated with the motor. Eventually such a relay fails.
Prior art vehicle heaters commonly have protection against excessive currents. However false error readings can result from starting the vehicle. When the ignition of the vehicle is first engaged, the starter motor starts and causes a voltage drop. The motor is cranked for a period of time and then starts, causing the alternator to begin operation. This causes a sharp voltage rise. The result can be a false indication that an overcurrent fault has occurred.
Another associated problem relating to prior art vehicle heaters is flame sputtering. Bubbles may occur in the fuel, for example. In fact the flame may be entirely extinguished on some occasions and the ignition for the heater may have to be used to restart the combustion. As a certain point, however, the lack of fuel may indicate a fuel leak or other fault in the fuel system requiring the heater to be shut down. Some prior art heaters do not have adequate means for distinguishing between occasional bubbles in the fuel and more serious problems.
Accordingly, it is an object of the invention to provide an improved vehicle heater, and control system therefor, which have a simple, but reliable means for controlling the speed of the motor.
Is another object of the invention to provide an improved vehicle heater, and control system therefor, which allow standard replacement motors to be utilized in heaters having different BTU outputs.
It is another object of the invention to provide an improved vehicle heater, and control system therefor, which have a main motor speed control system and a backup system in case the main speed control system fails.
It is another object of the invention to provide an improved vehicle heater, and control system therefor, which allow combustion to be confirmed without requiring a sight glass.
Is a further object of the invention to provide an improved vehicle heater, and control system therefor, which are capable of distinguishing between excessive currents which indicate a fault and situations caused by voltage changes during starting of the vehicle.
It is a still further object of the invention to provide an improved vehicle heater, and control system therefor, which are capable of reigniting the heater when the flame fails due to bubbles in the fuel or similar routine operational problems, but shut the heater down in the event that an actual fault, such as a leaking fuel line, is encountered.